S.C.
How old are your kids? Are they home all day with him?
We had a similar problems several years ago. My stepson (now 18) came to live with us during 5th grade. He had a lot of dysfunction in his life and he was a lot to handle as far as school, mentally, emotionally and even physically. He was on a special diet because he was extremely overweight. So my husband spent most of his time (when he wasn't at work) trying to help his son. There was A LOT of them 2 arguing and screaming at each other in front of our kids who were 3 & 4 at the time. They missed spending time with their dad and weren't used to the loud arguing. Their was also a lot of other disruption to their lives. My stepson would continually antagonize them and get them upset. We had to remove all the non-diet foods from the house because he would sneak them at night, so my kids missed all their usual snack foods. It was a very hard year to say the least!
I would suggest talking very honestly to your husband. He is probably going through a lot himself having his son there. I know my husband felt a lot of guilt about not being there for his son before this and blamed himself for his son's problems. Let him know your kids are having a hard time. Maybe even suggest to him, putting them in daycare. Maybe that will open his eyes to what a serious problem this is for you and your kids.